It was 22% of the total.
No project management role.
Architect designed builder build, there wasn't any relationship really and no communication between them.
I don't know why the builders haven't spotted the error,.or maybe if he did he didn't make a great deal of it because he completed a similar projects with a half brick wall without any issues (the BC was private and ours LA).
No, the architect never visited our house. He send his assistant to take the measurements.
We didn't have contact with the original SE, everything was through the architect, so no contract with the SE